1. Field
The following description relates to an optical module, and more particularly, to an optical module which is improved in structure to operate fast.
2. Description of the Related Art
As an optical communications system has been faster and smaller, a conventional transistor outline-CAN (TO-CAN)-type optical module has increasingly experienced electrical characteristic restrictions at a speed of 10 Gbps or more. This is because most of currently used TO-CAN packages have a signal flow path that is bent at 90 degrees when the TO-CAN package is connected with a flexible printed circuit board (FPCB).
FIG. 1 is a diagram illustrating an example of a connection between a conventional TO-CAN package and a FPCB. Referring to FIG. 1, a transmission line 11 of the FPCB 10 has a through-hole 12. After a lead pin 21 of the TO-CAN package 20 is inserted into the through-hole 12, the lead pin 21 and the through-hole 12 are bonded together by soldering, and thereby the lead pin 21 can contact the transmission line 11 of the FPCB 10. Accordingly, a signal flow path that is bent at 90 degrees is produced between the lead pin 21 and the transmission line 11. In this case, if the lead pin 21 is a data signal lead pin, an impedance discontinuity is generated in a contacting portion between the data signal lead pin 21 and the through-hole 12, which may degrade signal integrity.
A graph illustrated in FIG. 2 shows the effects of the impedance discontinuity on signal integrity. The graph shown in FIG. 2 is obtained under assumption that the FPCB 10 has a transmission range of 12 mm and a characteristic impedance of 50Ω. As shown in FIG. 2, in a high frequency band, a transmission loss S21 is growing and a reflection value S11 is increased, and hence it is apprehended that the structure shown in FIG. 1 is not effective to be used in a high frequency band.
Meanwhile, there has been introduced a TO-CAN package which has significantly improved the electrical characteristics by coating multiple insulating layers on a lead for fast operation. However, the manufacturing cost for TO-CAN package may be increased by the complexity of the structure.